1. Field of the Invention
This invention relates to a television receiver for reproducing video images having different aspect ratios and characters transmitted with the video images.
2. Description of the Prior Art
A first prior art television receivers having an oblong CRT (cathode ray tube) with an aspect ratio 16:9 is known. Such a prior art television receiver is originally provided for reproducing a video signal of the HDTV (high definition television) or the like. A second prior art television receiver with the oblong CRT capable of reproducing a video image having a different aspect ratio, namely, 4:3 in addition to the video image of 16:9 by using a compression or extension technique is known. In such a prior art television receiver, the user can reproduce video images having different aspect ratios by selecting a display mode from the standard mode for reproducing video image transmitted in the HDTV broadcasting and various modes for reproducing the video images having the aspect ratio of 4:3.
FIG. 5A is an illustration for showing a displaying condition in a prior art standard type television with a CRT having an aspect ratio of 4:3. FIGS. 5B to 5D are illustrations for showing displaying conditions in a plurality of displaying modes in the prior art television with an oblong CRT and are used in the description of the invention. In FIG. 5A, a circle is displayed on the standard type CRT having the aspect ratio of 4:3. If this video signal is displayed on the television receiver having the oblong CRT with the aspect ratio of 16:9 without a compression processing, the circle is displayed in an oval as shown in FIG. 5D (hereinafter, this mode is referred to as a full mode). Then, a compression processing for compressing the video signal in the horizontal direction is carried out to make the oval close to the circle. FIG. 5B shows this condition (hereinafter this mode is referred to as a regular mode). In this mode, though there are non-displayed areas, (i.e., black areas) at both sides of the CRT, the circle is correctly reproduced. FIG. 5C shows a condition that the video signal is displayed with the aspect ratio of the displayed image unchanged by over-scanning of the deflection circuit(hereinafter this mode is referred to as a cinema mode). That is, the video image is enlarged in the vertical direction compared with the full mode as shown in FIG. 5D. The user cannot watch the areas within the chain lines in FIG. 5C. However, this cinema mode provides the most strong appeal to the user. Therefore, this cinema mode is suitable for reproducing a cinema. In this mode about 80% of the original video image is reproduced. In other words, about 380 horizontal scanning lines are reproduced though the original video image includes about 480 horizontal scanning lines.
A third prior art television receiver having a function for reproducing character information with the video image superimposed on the oblong CRT in addition to the display modes of regular, cinema, and full modes mentioned above, is known. The character information is multiplexed on the video signal at horizontal blanking periods of 21st and 284th horizontal scanning lines in a form of the NRZ system, each piece of character information at each horizontal blanking period include 16 bit data. This prior art television receiver detects the character information, (i.e., caption information), at every horizontal blanking period multiplexed just after the vertical blanking period and displays the caption information on the CRT.
FIG. 6A is an illustration for showing a relation between the size of a prior art CRT having the aspect ratio of 4:3 and a region for displaying the caption information, namely, a character display region which is represented by the hatched portion. This drawing is also used in the description of the invention. In FIG. 6A, A denotes a height of the CRT; B denotes a width of the CRT; C denotes a height of the character display region which is equal to A.times.0.80; D denotes a width of the character display region which is equal to a.times.1.07; E denotes a vertical end position which is equal to A.times.0.10; and F denotes a horizontal end position which is equal to A.times.0.13.
FIG. 6B is an illustration for showing a map of displayed characters within the character display region. This drawing is also used in the description of the invention. The character display region includes 34 rows and 15 columns wherein the first and 34th columns are not used for displaying.
In the prior art television receiver, the caption information transmitted with the video signal is separated from the video signal by a caption information processing unit which decodes the separated caption information and superimposes characters on the video image in accordance with the decoded caption information. The conversion of the video image, (i.e., display size conversion), as shown in FIGS. 5B to 5D are carried out before superimposing the characters. This is because there is a tendency that a picture quality of the characters decreases due to conversion of the display mode, (i.e., changing of size of the display area). Particularly, conversion through a digital processing shows this tendency strongly. Moreover, there is a problem that the size of the characters will be too large or too small if the characters are superimposed before the display size conversion. However, in the television receiver with the oblong CRT, if the display conversion is carried out before the superimposing of the characters, there is a problem that the characters displayed in accordance with the caption information overflow the CRT or a suitable display region for displaying the characters. For example, if the characters are displayed in the cinema mode, upper and lower portions of characters slightly overflow the CRT having the aspect ratio of 16:9 in consideration of dispersion in displaying area of the CRT. In the regular mode, all characters can be displayed on the oblong CRT. However, right and left side portions of characters overflows the display area of the video signal because the video signal is compressed but the characters are not compressed in the horizontal direction. This provides unnatural feeling to the user.
Though FIG. 7 is a general block diagram of this invention, it is also applicable to a prior art television receiver with a caption information displaying function except that a size mode signal 31 is not supplied to a caption information processing circuit 8, and it is used for explanation of the prior art. FIG. 8 is a block diagram of a prior art caption information decoder shown in FIG. 7.
This prior art television has an oblong CRT 7 with an aspect ration of 16:9 and a displaying size conversion circuit for converting a video signal for a CRT with an aspect ration of 4:3 into a regular mode displaying size as shown in FIG. 5B.
A transmitted composite video signal including caption information (character information) is received by an antenna 1. The received composite video signal is converted to have an intermediate frequency by the tuner 2. The composite video signal having the intermediate frequency is amplified by an intermediate frequency amplifier which further includes a video signal detection circuit for detecting the composite video signal. The detected composite video signal is supplied to a video signal processing circuit 4 and to the caption information processing circuit 8. The video signal processing circuit 4 effects the Y/C separation, color reproduction, and matrix processings. An output of the video signal processing circuit 4 is supplied to a well-known displaying size conversion circuit 5. The displaying size conversion circuit 5 effects a displaying size conversion in accordance with a size mode signal 31. When the size mode signal indicates non-conversion, that is, the received video signal is for an oblong CRT 7 having an aspect ratio of 16:9, the display size conversion circuit 5 outputs the video signal from the video signal processing circuit 4 without conversion. When the display mode signal indicates another mode, that is, the received video signal is for a standard CRT (not shown) having an aspect ratio of 4:3, the displaying size conversion circuit 5 converts the video signal to reproduce the video signal to be reproduced as a video signal displayed on the oblong CRT having the aspect ratio of 16:9 as shown in FIGS. 5B, 5C, and 5D. That is, the video image is displayed on the oblong CRT 7 in a regular mode where there are non-displayed areas at both sides of the CRT 7, in a cinema mode where there are omitted areas at top and bottom portions, or in a full mode where all picture image displayed but the aspect ratio is unnatural. This processing is carried out using a digital compression technique of the video signal in the time base. An output of the displaying size conversion circuit 5 is sent to the RGB drive circuit 6 included a display portion 7a.
The caption signal processing circuit 8 separates the caption information from the detected video signal and outputs character color data signals R, G, and B indicative of color of characters to be displayed and a switching signal Ys indicative of switching between the video signal form the display size conversion circuit 5 and the character color data signals which are produced in accordance with the caption information. The character color data signals R, G, and B and the switching signal Ys are sent to the RGB drive circuit 6 in accordance with a caption information on/off signal 32 and the size mode signal 31. When the caption information on/off signal 32 indicates the non-conversion, the RGB drive circuit 6 outputs RGB drive signals produced from the video signal from the displaying size conversion circuit 5 to the CRT 7 because the switching signal Ys remains indicative of outputting only video signal. When the caption information on/off signal 32 indicates ON of displaying, the RGB drive circuit 6 outputs RGB drive signals with the character color data signals R, G, and B superimposed in response to the switching signal Ys to the CRT 7. A synchronizing circuit 9 separates horizontal and vertical signals from an output signal of the video signal processing circuit 4 and sends the horizontal and vertical synchronizing signals to a horizontal and vertical scanning circuit 10. The horizontal and vertical scanning circuit 10 has oscillators for producing a horizontal scanning signal of 15.75 kHz and a vertical scanning signal of 60 Hz in response to the horizontal and vertical synchronizing signals from the synchronizing circuit 9 respectively. That is, the horizontal and vertical deflection circuit 10 supplies horizontal and vertical deflection drive signals to a deflection unit 7b of the CRT 7 and supplies flyback pulses of the horizontal and vertical synchronizing signals to the caption information processing circuit 8. The caption information processing circuit 8 determines timing for positioning the caption information, (i.e., characters and marks on the picture plane of the CRT 7) in response to the horizontal and vertical synchronizing signals from the horizontal and vertical deflection circuit 10.
As shown in FIG. 8, the caption information processing circuit 8 comprises a front end unit 11, a decoding unit 12', and a display control unit 13'. The front end unit 11 receives the composite video signal from the intermediate frequency amplifier 3 and extracts the caption signal multiplexed in the composite video signal at 21st and 284th lines to send the caption signal to the decoding unit 12'. The decoding unit 12' decodes the caption signal and supplies display data to the display control unit 13' when the display of the caption information is commanded by a caption information on/off signal 32. The display control unit 13' supplies R, G, and B character signals indicative of color of the characters superimposed in the reproduced video image to the RGB drive circuit 6 with color of characters and timing of these signal determined in accordance with the received caption information, the horizontal and vertical signals supplied from the horizontal and vertical deflection circuit 10, and an oscillation signal produced by an oscillation circuit 13b to the RGB drive circuit 6. The display control unit 13' also supplies a switching signal Ys indicative of timing of switching between the R, G, and B drive signals and the R, G, and B character signals to the RGB drive circuit 6 with timing of the switching signal Ys determined in accordance with the received caption information; the horizontal and vertical signals supplied from the horizontal and vertical deflection circuit 10; and the oscillation signal.
The character decoding circuit 12a decodes the caption information to obtain decoded information of characters to be superimposed on the reproduced video image. The decoded information of characters is sent to a V RAM (random access memory for storing video data) 13c. The position data decoding circuit 12b decodes the caption signal to obtain positional information of a character within a display region of character information and sends the positional information to a display control circuit 13a of the display control unit 13'.
The memory 12c in the decoding unit 12' stores vertical start position data, horizontal start position data, size data indicative of vertical and horizontal sizes of a section for displaying one character to produce the display region as shown in FIGS. 6A and 6B.
FIG. 6A is an illustration for showing a relation between the size of a CRT 7 and a region for displaying the caption information, namely, a character display region 35 which is represented by the hatched portion.
FIG. 11 is an illustration for showing the vertical and horizontal start position data and vertical and horizontal size data. The vertical start position data Vposi indicates a vertical distance between the top left corner of the CRT 7 and the character display region 35. The horizontal start position data Hposi indicates a horizontal distance between the top left corner of the CRT 7 and the character display region 35. The vertical size data Vsize indicates a vertical size of one section included in the character display region 35, each section indicative of an area on which one character is to be displayed. The horizontal size data Hsize indicates a horizontal size of one section. More specifically, the memory 12c stores values set to counters included in the display control circuit 13a. That is, the memory 12c stores a value "a" for Vposi; a value "b" for Hposi; a value "c" for Vsize; and a value "d" for Hsize.
The memory 12c supplies the vertical and horizontal start position data and vertical and horizontal size data to the display control circuit 13a.
The display control unit 13' supplies the timing signal for displaying the character font data from the character ROM 13d at the commanded position with a suitable size. That is, the display control circuit 13' produces the timing signal using the horizontal synchronizing signal Hsync to determine timing of the vertical displaying of the character and using the clock signal outputted from the oscillation circuit 13b to determine timing of displaying of the characters in the horizontal direction. The oscillation circuit 13b is controlled to output the clock signal 37 in response to the vertical synchronizing signal Vsync. As mentioned, the display control circuit 13a controls position of the character display region.
FIG. 9 shows a flow chart of an operation of the prior art decoding unit 12'. The decoding unit 12' includes a microprocessor (not shown) and executes a stored program as shown in flow chart shown in FIG. 9. Processing starts at step 101. In the following step 102, a flag indicative of displaying/non-displaying of the caption information (DSP.FLG) is reset. In the following step 103, the memory 12c sets data of Vposi=a, Hposi=b, Vsize=c, and Hsize=d to the vertical start position and size counters and the horizontal start position and size counters of the display control circuit 13a. Then, processing proceeds to step 104.
In step 104, a decision is made to as whether or not the caption information on/off signal 32 is present. In the absence of the caption information on/off signal 32, processing returns to step 104. In the presence of the caption information on/off signal, processing proceeds to step 105. In step 105, a decision is made as to whether or not the displaying/non-displaying flag of the caption information (DSP.FLG) has been set. If the displaying/non-displaying flag has been set to 0, the flag is set to 1 in step 106. In the following step 107, the displaying of the caption information is started. That is, the character decoding circuit 12' starts outputting the decoded caption information. If the displaying/non-displaying flag has been set to 1, the flag is set to 0 in step 108. In the following step 109, the displaying of the caption information is stopped. That is, the character decoding circuit 12' stops the outputting of the decoded caption information.
As mentioned, the prior art television receiver having the caption information processing unit, did not control the caption information processing unit in accordance with the display size conversion, so that there are problems that a portion of the character information cannot be displayed and the display position of character information deviates from the correct position.